[Unclenick]

Agree with HiBC on the drop tubes. They can create a surprising amount of additional space if you need it. If you don't need it, though, you may find more consistent ignition without. Federal's original 168 grain Sierra GM Match .308 load of 4064 was just slightly compressed and was very good. I haven't pulled one of their current RL15 loads to see if they are compressed? I don't know Federal's powder drop, either. Probably more than most hand loaders use.

Sinclair has drop tubes for different powder measure brands if you want a plug-in. Midway used to have (and probably still does) a funnel set with a drop tube. There are others.


Steve4102,

There is no exact formula. If you look at Accurate's web site (they are the only brand I know that provides this data) and click on one of their powders, you'll see a bulk density number come up. For Accurate 2520 it is +/- 3.6%. For Accurate 4064 it is +/- 3%. For Accurate 4350 it is +/- 2.2%. So, even if you stick to the same brand of case, the fill could swing 7.2%, 6%, or 4.4% extreme spread, respectively, depending what powder lot number you bought a pound of and how much it was tossed around in transport.

Then, of course, you have brand to brand case variation. A Winchester .30-06 has about 2.5% more usable powder space under a 168 grain SMK bullet, for example, than a 12 grain heavier Remington case does. Since SAAMI only regulates the exterior dimensions of cases, the manufacturers are free to design as much space in as they please, just as long as it still holds up under SAAMI proof pressures.